This also addresses an issue where the goroutine was not breaking out of
the loop parsing the options, instead it was only breaking out of the
switch statement.
Because of the requirement of storing multiple ports, Announce.Port has
been abolished and Announce.IPv4/IPv6 have been replaced with the
Endpoint type. HTTP has been updated to support this model. UDP has been
updated to support the latest draft of BEP45 and most of the
optional-types described in BEP41.
